The purpose of Core B, the In Vivo Experimentation Core (IVEC) is to provide logistical support, expertise and guidance for examining Ets gene function in vivo by using the mouse as model organism. This core consists of five components, including, (i) maintenance and husbandry of transgenic mouse strains, (ii) generation of new transgenic models, (iii) morphometrical and histological analysis of mammary gland (iv) cryopreservation, and (v) reporter gene analysis. This core structure ensures access to state-of-the-art technology to for studying mammary gland tumor development and metastasis in existing and new transgenic mouse models. Centralizing in vivo experimentation has several distinct advantages over individualized experimentation, including greater efficiency, uniformity of experimental conditions (which facilitates direct data comparison), providing a source of inspiration for developing plans or hypotheses for cross-project experimentation (e.g. crossing of mutant strains), and rapid adaptation to emerging new methodologies. Consequently, this core will be a dynamic unit with maximal responsiveness to the needs of the individual projects both at present, and as they arise during their progress.